Probing bulk viscosity in relativistic flows

TL;DR

This paper establishes an analytical link between kinetic relaxation rates and bulk viscosity in relativistic fluids across various regimes, validated through theoretical and numerical methods, with implications for quark-gluon plasma experiments.

Contribution

It provides a comprehensive derivation connecting relaxation rate and bulk viscosity using Chapman-Enskog and Grad's methods, and validates these results with numerical simulations.

Findings

Analytical expression for bulk viscosity across relativistic regimes

Validation of Chapman-Enskog approach with benchmark flow

Numerical simulations indicating effects of bulk viscosity in quark-gluon plasmas

Abstract

We derive an analytical connection between kinetic relaxation rate and bulk viscosity of a relativistic fluid in d spatial dimensions, all the way from the ultra-relativistic down to the near non-relativistic regime. Our derivation is based on both Chapman-Enskog asymptotic expansion and Grad's method of moments. We validate our theoretical results against a benchmark flow, providing further evidence of the correctness of the Chapman-Enskog approach; we define the range of validity of this approach and provide evidence of mounting departures at increasing Knudsen number. Finally, we present numerical simulations of transport processes in quark gluon plasmas, with special focus on the effects of bulk viscosity which might prove amenable to future experimental verification.